The American sunglass industry has done a good job of regulating itself. The world has followed. The industry has seen to the use of good science, but it is appropriate to know which claims of superiority have validity and which are shaded distortions, pun intended.
Let’s start by considering the UV filtration aspect of sunglasses.
The prefix “ultra” means the light wavelengths are too violet, i.e. too short, for us to see. Light wavelengths are measured in nanometers, i.e. nm’s, and there are three divisions of UV:
UVA (400 to 315nm)
UVB (315 to 280nm)
UVC (280 to 100nm)
Ninety-five percent of the UV reaching earth is UVA. Virtually all the reputable sunglasses filter it.
Shorter wavelength UV has higher energy and is more damaging than longer wavelengths, but short UV is also more easily diffused or scattered.
UVB is responsible for the production of Vitamin D in the human body. Unfortunately it is associated with some health problems such as skin cancer and cataracts. The scientific community sort of accepts UVB as the prevailing culprit in skin cancer and other sun related health problems even though definitive studies directed at UV wave bands are not easily found.
The scientific community accepts ozone depletion and increasing UVB as a man caused fact, although both have been waning for the past few years presumably because of CFC (chlorofluorocarbon) regulation. For purpose of this blog I’ll accept science’s conventions on these matters. Still I think it is fair to say that variables other than UV have not been given serious consideration.
UVC is even more damaging than UVB. Certain professions, e.g. welders and scientists studying ultraviolet light, get exposed to UVC, but it is not from the sun. Only three to five percent of UVB reaches the earth. There is no UVC that gets down here.
UVC filtration by sunglasses has no human benefit. Advertising glasses that filter it is at best a misinformed ad department. At worst it’s deceptive advertising.
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